Method of ascertaining the actinic value of light for photographic purposes



Nov. 11 1924. 1,514,665

E. G. KEsLlNG METHOD OF ASCERTAINING THE ACTINIC VAL/,UE OF LIGHT FOR PHOTOGRAPHIC PURPOSES Filed .ly 17, 1920 ATTO R N EY Patented Nov. ll, i924. i u A *MNTE- Siti ELMER Gr. KESLNG, F BLOQMFEELD, MISSOURI.

METHOD 0F ASGERTAINING THE ACTINIC VALUE 0F LIGHT FOR PHOTOGRAPHIC YURPDSES.

Application filed Julyl?, 1929. Serial No. 396,921.

To all 107mm t may concern. with a lens. and the tube and lens are ar- Be it known that l. ELMnn G. liner-ING, ranged at an angle to the longitudinal axis citizen of the United States, residing at or". the in'iagg'e producing part so that the line Bloomfield, in the county of Stoddard and of sight of the image producedon the screen State oililissouri. have invented new and is out ot line with the optical axis ot the 60 useful Methods ot' ascertaining the Actinic image producing part of the structure. This Value of Light for Photographic Purposes, provides for a clear view ot the image pro of which the following is a specification. jected on to the screen within the structure rThis invention has reference to the method and of' the standardized light producing` lo of ascertainingythe act-inic value of light for means, ttor-comparison. so that no direct con- 65 photographic purposes and its object is to fusing view is obtained et any high lights both ascertain such actinic value by a romwhich may appear in the scene to be photoparison 'ot the image with a light source of graphed and which might otherwise inter- X'ed value and to provide an instrument tere with the correctness oit the comparison.

whereby the actini'c'value may be readily as- The invention will be best understood 70 certained in order toindicate the proper setfrom a consideration of the following detin'g of the camera. tailed description taken in connection with In accordance with the invention prothe accompanying drawings `iorming part of vision is 'made'forprojecting an image of the this specification. with the understanding, scene about to be photographed upon a however` that the invention is not confined 75 screen or background with the line ot-vision to any strict conformity with the showing in of the image so produced at an angle to the the drawings, but may be changedl and modiaxis of the image on to the screen, whereby tied so longI as such changes and modifica the image on the screen may be viewed out tions mark no material departure from thc of line 'with the source of light and at the salient teaturt-xs of the invention as eX- 80 'samey time the viewed image may be compressed in the appended claims.

pared with another v'source of light of con .ln the drawings:

stant value. By modifying the intensity of Fig'. l is an elevation ot an exposure the image of the view to be photographed meter embodying the invention.

until such intensity shall agree with the Fig. 2 is a longitudinal section ot the 85 Vsource ot `light of constant intensity, or structure shown in Fig. l but drawn on a shall be brought to a chosen comparative inlarger scale. tensityfand by providing means whereby they Fig 3 is a longitudinal section on the line adjustment oit the parts to produce the de- 3 3 ot Fig. 2 with some parts shown in sired intensity may be indicated, the proper elevation. e0 setting for the light controlling parts of the Fig. 4e is an elevation oi the diaphragm camera are shown. j end of the exposure meter.

In 'the apparatus constructed in accordj Fig. 5 is a section on the line 5 5 of ance with the invention. which is not herein big. 2.

4o claimed, there is provided a small camera-v T g. 6 is a section on the line 6--6 of 95 il. ylike structure having an adjustable dia- Fig. phragm, preferably of theoiris diaphragm llig.V T is a Atace view ot the image screen form; and the image may be producedi in removed Yfrom the device. conjunction with the diaphragm, by a sim- Referring to the drawings, of which Fig.

.plelensthrowing the image ofthe scene or l is drawn at about natural size and the 10o "object to be photographed upona light transother figures are enlarged so as to be above "mitting screen havinga plurality of transnatural size, there is shown a tubular" casinitting"portions ot different lighttransmiting member i having an extension 2 at one 'tingvalues `["issociat'ed with such a screen end at `an angle to the longitudinal central 5o lso "as to be readily utilized `for comparison aXis of the main portion ot the casing mein- 105 purposes, is a surface provided with seltberl. rEhe extension 2 is provided with ya luminous'materal such as one of the radium section f3 telescopingin the extension 2 thus Compounds, y permitting a limited amount of longitudinal Connected with the camera device is an adjustment of the telescoping section 8 in 5a "eye piece comprising an appropriate tube v"the angle extension 2. 110

lVithin the portion of section 1 of the instrument there is a sleeve 4@ serving as a reinforcing or stiffening sleeve and also Ifor other purposes1 and at the forward end the sleeve a'has an internal screw threaded part 5 to receive an external screw threaded neck 6 on a head 7 in which there is mounted a lens 8 of appropriate character to project an image to the rear end of the sleeve 4L where the latter is provided with an inturned flange 9 for about half its circumference and a head 10 of about half of the cross sectional area of the sleeve1 the remainder of the corresponding end of the sleeve having an opening 11 therethrough unobstructed by any portion of the sleeve.

In the angle extension 2 there is a bear-- ing sleeve 12 in the longitudinal axis of the casing section 1, this bearing entering the interior of the casing and extending beyond the exterior thereof. Mounted in the sleeve 12 is a rock shaft 13 carrying a disk 14: capable of turning with the shaft 13 and lodged against the head 9 and l0 of the sleeve L1. T he disk 14 is or may be formed of frosted Celluloid or other translucent materia-l with about one-half, indicated at 15, thicker than the other half, indicated at 16 and while not necessarily confined to any particular materia-l is preferably made of ce-lluloid of green tint, the difference in thickness of the two halves of the disk producing a correspo-nding difference in light transmitting power, for the density of the thicker portion is greater than that of the thinner portion.

The end of the shaft 13 beyond the extension 2 is provided with a manipulating handle 17 of appropriate form. lThe celluloid or other light transmitting disk, may be frosted or otherwise rende-red translucent for use as a photographic screen sothat an image may be projected thereon by the lens 8 so as to be readily observed by looking through the eye-piece lens 18 mounted in the tube 3, which latter, outside of the lens 18, has a flaring eye shade 19 to exclude extraneous light. Moreover, the eye-piece end of the tube 3 on opposite sides of the lens 18 is furnished with diaphragme 20, 21, serv-- ing to sharpen the image seen by the eye.

At one side of the shaft 13 the angle portion 2 of the body l contains a plate 22 dividing the field of view, as seen through the lens 18, into two parts. The division plate 22 has an angle end 23 hiding a portion, approximately one-half, of the disk 14 from view, and the angle extension 23 carries a sheet* or coating 24 of self-luminous material of the radium type, as, for instance, a radium luminous material obtainable on the market under the trade name of Undarl. This particular material is suitable for the purposes of the invention since it has the property of remaining constantly luminous Without the aid of external light and consequently furnishes a field of standard luminosity for comparison. The plate or wall 22 provides a division between the luminous sheet or wall 24; and a light image projected upon the screen 14 appearing on the other side of the wall 22 away from the luminous sheet or field 2li, In order to hold the wall 22 in place the tube or bearing 12 is provided with a clip 25 bent over the wall 22.

The head T has secured to it an iris diaphragm 26 provided with the customary hood 2T permitting access of light to the iris diaphragm, but excluding stray rays of light, whereby to prevent glares. The moving parts of the iris diaphragm are controlled by a finger piece 28 in the customary manner. The iris diaphragm need not differ from such structures as are found on the market and hence requires no special l description, the office of the iris diaphragm being to gradually vary at will the intensity of the light entering the body of the instrument and consequently' the brilliancj7 and sharpness of the image projected by the lens 8 upon the field received upon the disk l/Vhen the instrument is used to indicate the time of exposure of a photo-sensitive surface the end of the instrument containing the lens 8 is po-inted toward the scene to be photographed and adjusted so that the desired part of the scene becomes visible upon that part of the screen 14- opposite the open ing 11. If they scene be particularly brilliant, the denser portion of the screen 14: is moved into the line of vision. if the light be dimmer then the thinner portion 16 of the screen is moved over the opening 11, by a suitable manipulation of the handle 1T. Having located the part to be photographed the iris diaphragm 26 is adjusted by means of the finger piece 28, which also serves as a pointer, so that the brilliancy of the image is brought into conformity with thebrilliancy of the light emanating vfrom the radio-active material 24 on the side of the division wall or diaphragm 22 remote from thev openinglle a Having brought the image of the scene to' be photographed intoagreement with the standard light emitted. from the radio-active material, the instrument is removed from the eye and the number on the scale 29 opposite which the finger o-r pointer 28 is found is observe-d and this number will be found to be the timeV of exposure of the sensitive photograph'surface to obtain a properly exposed negative.

v The light emanating from the radio-active material is of a greenishr blue tint and it is for this reason that thefscreen upon which the light image of the scene to` be photographed is projected is given a similar tint, but With the different parts of different thicknesses to produce differences in density, whereby brilliant images are toned down in order that a brilliant image may appear as ,of the same intensity as the self-luminous `field, or, in case of the light being poor, the image of the scene to be photographed may be brought into engagement With the selfluminous material Without toning down.

If the line of sight from the eye lens 1S to the screen 14C and so on through to the eld of the image forming lens 6, were a straight line of sight, then the opening through the diaphragm 26 Would appear more brilliant than it should. However, by making the line of sight from the eye lens 18 to the screen opposite the opening 11 at an angle tothe optical axis of the lens 8, the eye of the observer is out of line with the opening through the diaphragm 26, and the glare spot which would otherwise appear is not seen and consequently does not deceive the observer in comparing the image appearing on the screen opposite the opening 1i with the light image of the luminous material.

The time scale 29 is or may be proportioned to a chosen stop on the camera shutter, say stop No. 16, so that when it is determined that a certain time of exposure is necessary for the light available, it is an easy matter to calculate the amount of exposure necessary for larger or smaller stops.

llihe casing may be conveniently provided with tables for guiding the operator in the use of the instrument, but it is deemed unnecessary to illustrate such tables, for they may vary in accordance with the stops employed and with other conditions, and such tables may be readily Worked out by the manufacturer. i

The instrument with the exception of the lenses and luminous material, may be made of sheet metal yfinished in any desirable Way. In use the luminous material provides a constant source of light for comparison with the image seen upon the screen 14, and such image may be brought into conformity with the luminosity of the luminous material by a variation in the diaphragm opening of the iris diaphragm 26, whereupon the position of the pointer 28 on the scale 29 will then indicate the time of exposure in the camera of the sensitive surface to the scene to be photographed. The necessary lengths of exposure for other stops than the one to which the instrument is standardized are readily ascertained.

What is claimed is:

1. rlhe method of ascertaining of light for photographic purposes, Which consists in projecting an image of an object or scene upon a screen, comparing the image on the screen with a self-luminous surface of constant intensity located in proximity thereto, adjusting by means of a pointer Working over a predetermined scale the illumination of the screen until the image of the object or scene to be photographed is brought into agreement With the selfluminous surface, and then noting upon theV scale the indicated time of exposure of a photo-sensitive surface to the scene to be photographed.

2. The method of ascertaining the time of exposure of a photo-sensitive surface to a scene to be photographed, which consists in projecting an image of the scene upon a screen, comparing the image with a selfluminous surface of const-ant intensity, cutting down the illumination of the field upon the screen until equaling the luminosity of the luminous surface and nally noting on a predetermined scale of times of exposure the exposure time indicated by the adjustment of the luminosity of the image to that of the self-luminous surface.

3. The method of ascertaining the strength ofy light producing an image, Which consists in projecting the image upon a surface, stopping down the light of the image until the image equals a given luminosity, with the, image viewed at an angle to the optical axis of the image, and then noting upon a scale provided for the purpose the time of exposure of a sensitive surface in a camera, determined by the position of an indicator associated with the scale and moved in the act of stopping down the illumination of the image.

ln testimony, as my own, have nature. i

that I claim the foregoing hereto afiixed my sig ELMEB G. KESLING.

the strength n 

